CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS Percentage	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues
Total revenue (as a percent)	100.00%	100.00%
Cost of revenues
Labor and other operating expenses (as a percent)	68.20%	65.00%
Depreciation, depletion and amortization (as a percent)	11.80%	11.60%
Total cost of revenues (as a percent)	80.00%	76.60%
Gross profit (as a percent)	20.00%	23.40%
Selling, general and administrative expenses (as a percent)	7.10%	7.20%
Operating profit (as a percent)	12.90%	16.20%
Other (income) expenses
Interest expense (as a percent)	0.20%	0.10%
Interest and other income, net (as a percent)	(1.00%)	(0.10%)
Total other (income) expense (as a percent)	(0.80%)	0.00%
Income before income tax expense (as a percent)	13.70%	16.20%
Income tax expense (as a percent)	1.60%	4.10%
Net income (as a percent)	12.10%	12.10%
Lime and limestone operations
Revenues
Total revenue (as a percent)	98.40%	98.70%
Natural gas interests
Revenues
Total revenue (as a percent)	1.60%	1.30%